Fun x86 encoding tricks: when adding an immediate value of 128,
use a SUB instruction instead of an ADD, because -128 can be
encoded in an 8-bit signed immediate field, while +128 can't be.
This avoids the need for a 32-bit immediate field in this case.
A similar optimization applies to 64-bit adds with 0x80000000,
with the 32-bit signed immediate field.
To support this, teach tablegen how to handle 64-bit constants.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57663 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index 16dc366..f44b918 100644
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -2911,6 +2911,17 @@
// Some peepholes
//===----------------------------------------------------------------------===//
+// Odd encoding trick: -128 fits into an 8-bit immediate field while
+// +128 doesn't, so in this special case use a sub instead of an add.
+def : Pat<(add GR16:$src1, 128),
+ (SUB16ri8 GR16:$src1, -128)>;
+def : Pat<(store (add (loadi16 addr:$dst), 128), addr:$dst),
+ (SUB16mi8 addr:$dst, -128)>;
+def : Pat<(add GR32:$src1, 128),
+ (SUB32ri8 GR32:$src1, -128)>;
+def : Pat<(store (add (loadi32 addr:$dst), 128), addr:$dst),
+ (SUB32mi8 addr:$dst, -128)>;
+
// r & (2^16-1) ==> movz
def : Pat<(and GR32:$src1, 0xffff),
(MOVZX32rr16 (i16 (EXTRACT_SUBREG GR32:$src1, x86_subreg_16bit)))>;